What it shows
A single white flower can turn two colours when its stem is split and each half drinks a different dye. It shows that water travels in separate channels all the way up to the petals.
The science
The stem holds many xylem tubes that run from the base to the petals without mixing very much. Each half of the split stem sucks up the dye in its own glass, and the colour is carried along the separate tubes to the petals above that half. Water leaves through the petals by evaporation and pulls more coloured water up behind it.
Materials
Cost: under Rs 50. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- A white flower with a long stem, such as a white carnation, chrysanthemum or tuberose
- Two small glasses or bottle caps
- Red and blue food colour (a few drops each)
- Water
- A blade or sharp scissors for the adult only
- A notebook for a time log
Safety
For this project: An adult must split the stem with a sharp blade. Wash your hands after touching food colour.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
All the safety rulesStep by step
8 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
Colour half a glass of water deep red and another half glass deep blue, and stand the two glasses side by side.
Ask an adult to trim the flower stem to about 15 cm and split it upward from the bottom for about 7 cm, keeping the two halves attached above.
Put one half of the stem into the red glass and the other half into the blue glass, bending them gently without breaking the stem.
Place the flower in a bright, airy spot, and check it every hour for the first four hours.
Write the time at which you first see colour in the veins of the petals.
After 24 hours, look at the petals and note which side of the flower turned red, which turned blue and where they meet.
Take a photo or draw the flower, colouring the petals as they now look.
Repeat with a whole stem in one colour and compare how fast it colours in a warm spot.
What you should see
The petals above the red half turn pink to red, the ones above the blue half turn bluish, and a mixed patch may appear in between. This shows each half of the stem feeds its own side of the flower.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1Why does the white flower change colour?
It drinks coloured water through its stem and the dye is carried to the petals.
2Why can one flower show two colours?
Water travels in separate tubes, so each half of the stem feeds the petals above it.
3What is the part of the stem that carries water called?
The xylem.
4Why does the colour appear first in the veins?
Because the veins hold the tubes that bring the coloured water.
Take it further
Split the stem into three parts and use red, blue and yellow dye to see if the petals can show three regions.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.
Free ebooks for this project
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